Arithmetic methods
Related code
class Dog:
"""Represents a dog.
attributes: name: str, age: int, energy: int
"""
def __init__(self, name, age, energy):
self.name = name
self.age = age
self.energy = energy
def __str__(self):
return f'Name: {self.name}, Age: {self.age}'
def __gt__(self, other):
return self.age > other.age
def add(self, other):
new_dog = Dog(self.name + other.name, self.age + other.age, self.energy + other.energy)
return new_dog
murki = Dog("Murki", 2, 50)
reksi = Dog("Reksi", 1, 50)
Instead of using add to create a dog which is as old and has as much energy as two dogs,
it would be better if we could do dog1 + dog2. Let's try to apply + two murki
and reksi:
>>> murki + reksi
TypeError("unsupported operand type(s) for +: 'Dog' and 'Dog'")
Python doesn't know how to add them, we have to tell Python how it should add two dogs, just like
we told add method.
In order to be able to apply arithmetic operators to dogs we have to overload the following dunder methods:
__add__(addition)__sub__(difference)__mul__(multiplication)__div__(division)__pow__(power)
class Dog:
...
def __add__(self, other):
return "__add__ method is activated"
...
Now whenever we apply + to two dogs, this method is activated:
>>> murki + reksi __add__ method is activated
We proved that __add__ is activated when we apply + to two dogs.
Now let's give meaning to this operator when applied to dogs. We already have an idea of what
does adding two dogs mean for us, creating a dog as old and with as much energy as the input dogs.
This is the implementation of add method. So let's just rename this method:
class Dog:
...
def __add__(self, other):
new_dog = Dog(self.name + other.name, self.age + other.age, self.energy + other.energy)
return new_dog
...
>>> sharki = murki + reksi >>> print(sharki) Name: MurkiReksi, Age: 3 >>> sharki.energy 100
Arithmetic operators don't make much sense in the case of dogs, but for testing purposes you can go on implementing other arithmetic dunder methods.